This invention relates to the removal of sheaths from catheters and, more particularly, to a novel and highly-effective method and apparatus for removing a hollow, open-ended sheath from a position enclosing at least a portion of a catheter which has been inserted through the sheath with a close tolerance and introduced into a human body thereby.
The technique of percutaneously entering the human vascular system with a thin walled flexible sheath was first described by Desilets and Hoffman in 1965. The sheath is hollow and open at both ends and placed into the blood vessel with the aid of a relatively stiff introducer which is initially housed within the sheath and which is removed after the sheath has been inserted. The sheath then acts as a passageway for the insertion of many types of catheters into the vascular system. This includes the placement of intra-aortic balloons, for example, of the types as described in U.S. patent to Hanson and Wolvek U.S. Pat. No. 4,327,709.
The percutaneous introduction of catheters via introducer sheaths has become an established practice in angiography. Angiography catheters in the neighborhood of 4 to 7 French (0.053"-0.092" in diameter) are routinely introduced through introducer sheaths. The advent of the percutaneous intra-aortic balloon has increased dramatically the use of introducer sheaths, as well as their size. These sheaths now accommodate balloon catheters ranging from 8.5 French to 12.5 French (0.112"-0.164" in diameter).
When the introducer sheath is permitted to remain within the artery, surrounding the treatment catheter, the total diameter of the device within the blood vessel is increased by twice the wall thickness of the sheath plus twice the required catheter clearance. In practice, the presence of the introducer sheath may add up to 0.050" to the diameter of the catheter.
Since many treatment catheters such as intra-aortic balloon catheters or ECG pacing lead catheters have enlarged hubs or electronic connections at their proximal ends, the sheath cannot be removed simply by pulling it back along and beyond the catheter and discarding it. In these cases the sheath must actually be cut away or split away from the enclosed catheter. This is generally done by using a scalpel or scissors to cut the sheath away from the catheter. However, the risk of damaging the catheter is always present in such a procedure. The problem being recognized, several attempts have been made to develop a sheath that can be peeled away from the catheter.
The Desilets-Hoffman "Peel Away" introducer sheath has a split proximal end which terminates in two soft flexible "handles." The length of the sheath is scored to encourage splitting away of the sheath simply by pulling the two handles in opposite directions. Another split sheath is the Littleford/Spector introducer (U.S. Pat. No. 4,166,469). This introducer sheath has a T-shaped handle which is reduced in thickness at its centerline, thereby allowing the T-shape to be split by manual pressure. A small punched hole in the sheath material immediately below the splittable portion of the "T" handle, shallow longitudinal groove in the sheath material, perforations, holes, through cuts and reduced wall thicknesses have been described to encourage the longitudinal tearing of the sheath.
Other peelable catheter introducer sheaths have been disclosed which are scored so as to be splittable and which comprise a slidable sleeve to prevent the splitting until the sleeve is slid down the catheter by the physician. These are described by King et al in U.S. Pat. No. 4,412,832 and Boarini et al in U.S. Pat. No. 4,411,654. In both patents no hub assembly is present to form a portion of the introducer sheath.
All of these attempts to solve the problem deny the physician the use of a conventional introducer sheath having a hub containing a female luer at its proximal end. The female luer is present in all non-splittable, conventional introducers and serves multiple important functions. Among these functions is the ability to lock the introducer dilator within the introducer sheath during the actual insertion, by means of their respective luer tapers. After removal of the introducer dilator, the female luer of the introducer sheath can be used for the attachment of a three-way stopcock and syringe for such purposes as blood sampling, the injection of radiographic contrast material, or merely to close the introducer off from the atmosphere. The female luer hub also serves as a "handle" to support the introducer sheath while inserting the catheter within it and helps to control bleeding during the insertion of the catheter.
In addition, the splittable sheaths described above have the potential of splitting accidentally, either because of the internal pressure generated by the passage of a tightly fitting catheter or because of the accidental separation of the splittable handles by the physician. Accidental premature splitting of the sheath while in an artery could result in loss of blood because of the high blood pressures and flows in the arterial system.